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R. Legras, H. Rouger; Just Noticeably Levels of Aberration Corrections. Invest. Ophthalmol. Vis. Sci. 2008;49(13):993.
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Customized contact lenses, intraocular lenses and refractive surgery are now being developed to correct the main higher-order aberrations present in the eye which are spherical aberration (SA), coma and trefoil to provide normal people with an improved vision. We studied, using an Imagine Eyes CRX1 device, whether a partial or a full correction of the three main aberrations is necessary to give a noticeable improvement of the subjective vision quality.
Subjects viewed calculated images through a 5.5-mm artificial pupil and an adaptive optics system to correct their eye aberrations. The images were obtained by convolving an original 0.4-logMAR E-letter with a polychromatic point spread function calculated with a numerical eye model including the desired wavefront defined on a 6-mm pupil size. Three subjects made side-by-side comparisons between the non-corrected aberrations image (NCAI) (e.g. typical higher-order aberration up to 6th radial order of 0.35-µm RMS, including 0.128, 0.169 and 0.133-µm respectively of SA, coma and trefoil) and one of the 27 partially corrected variant images (e.g. no, half or total correction of each of the 3 main aberrations). Each of the 27 images was compared 50 times to the NCAI. A percentage (e.g. subjective preference, SP) lower than 25%, meant that the partially corrected variant images appeared noticeably clearer than the NCAI.
The subjective preference was found to be significantly correlated with the remaining RMS level of aberrations (r=0.82) and the MTF integrated between 5 and 15-c/deg (MTFa, r=0.92). An analysis of variance was carried out to compare the change in subjective preference with each aberration correction conditions. A significant difference of SP was found with change of SA correction (F=5.32, p=0.014) and with change of coma correction (F=5.92, p=0.009) but not with the correction of trefoil (F=2.23, p=0.133). A noticeable improvement in the image quality was found when the following two conditions were fulfilled: a half or full correction of SA and coma. We measured that 0.13-D of defocus is just noticeable (e.g. a SP of 25%) when testing in the same conditions.
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